System and method for efficient and expedient delivery of hot water

ABSTRACT

A system and method for detecting and anticipating fluid flow in a pipe utilizing a sensor, a processor, and a time base.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application 60/672,159 filed Apr. 15, 2005 and entitled “SYSTEM AND METHOD FOR EFFICIENT AND EXPEDIENT DELIVERY OF HOT WATER.”

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to the mechanical and electrical arts. In particular, the invention relates to systems and methods for detecting fluid flow and for anticipating demands for fluid flow.

2. Description of Related Art

Modern plumbing systems typically provide both hot water and cold water to various locations in a house or other structure. Water at these locations can be used for many purposes, for example washing, bathing, laundry, drinking and cooking. Each location where water is used has an outlet controlled by valves, also sometimes known as faucets, taps, or spigots. A valve can control the flow or mix hot and cold water to the outlet. Hot and cold water are supplied to the outlet location by plumbing systems consisting of various types of pipe or plumbing lines configured into a supply network. For example, many household systems supplying potable water use copper pipe or galvanized iron pipe. Hot and cold water are typically supplied by separate pipes. “Cold” water is actually water supplied at ambient temperature, near the temperature received from the water supply, well, or utility. “Hot” water is obtained by routing water from the utility, supply or well to a heating device before sending to the hot water plumbing lines.

A problem arises where a hot water outlet is remote from the water heating device because a volume of water at a temperature lower than that provided by the water heating device exists in the interconnecting pipes.

During periods when hot water is not flowing in a hot water pipe, the temperature of the stagnant water in the pipe approaches ambient temperature. A user opening a remote outlet such as a valve or faucet must therefore wait for the relatively cool water in the pipe to be purged before hot water reaches the outlet. In conventional systems, the purged relatively cold water is allowed to flow down the drain and is therefore wasted.

Thus conventional systems not only waste water, but they require a user to wait until relatively cold water in the pipe or line is purged. These problems are aggravated in cooler ambient temperatures or in larger homes or buildings with correspondingly larger volumes of water stored in their respective water plumbing systems.

Insulating the hot water lines is a solution known in the art. This solution slows the cooling of the water in the hot water lines; however, the water cools eventually and the problems of delay and waste remain.

Recirculating solutions are also known in the art. Here, the cooler water in a hot water line is removed to the cold water system for reuse, rather than discarded. Some recirculating systems are implemented by installing an additional plumbing line, running from the furthest point in the hot water distribution line back to the hot water heating device. Thus the hot water line and recirculation return line form a complete circuit through the hot water heating device.

In a typical recirculation system, a recirculation pump draws the cooler water from the hot water supply lines and moves it into the hot water heating device, simultaneously drawing hot water into the hot water supply line. This fills the hot water supply system rapidly with hot water. The effect is to provide hot water to an outlet much more quickly when the pump is running, and to avoid wasting water.

However, a difficulty arises in trying to determine when to activate the recirculation pump. Running the pump continuously is highly inefficient because the entire hot water plumbing system is continuously replenished with hot water, continuously remains hot and continuously transfers heat to the surroundings even when hot water is not needed by users. In many hot water systems, the periods of use are intermittent and shorter than periods of non-usage. Continuous pump operation also consumes electricity and may contribute to wear on pipes and lead to repairs or early replacement of plumbing systems and related components. Pump life is also unnecessarily consumed by operation during periods when there is no user demand for hot water.

The United States Department of Energy has identified control of hot water recirculation systems as a challenge and inadequate control of such systems as a source of energy loss. Their website, in a summary of the Building America Expert Meeting held in July 2004 states:

-   -   “Hot water recirculation systems contribute to large energy loss         if not adequately controlled. Energy codes that require these         systems should be changed to also define acceptable methods of         control.”     -   “http://www.eere.energy.gov/buildings/building_america/rh_(—)0704_home_improv         e.html)         Intermittent operation of the recirculation pump can reduce         energy and water waste; however, determining when to operate the         pump is an unsolved problem.

Some conventional systems operate the pump intermittently, using a temperature regulation system. In this system the pump is turned on when a single temperature measured at some point in the system falls below a fixed threshold value. This type of system keeps the entire hot water circuit at an elevated temperature at all times. This scheme suffers from much the same energy wasting limitation as continuous operation, in that energy is lost from the pipes continuously. However, it does reduce the delay that occurs before hot water is delivered to an outlet.

Other known systems use a timer to operate the recirculation pump during selected periods. These timers are typically electromechanical having a limited number of user selectable on and off events during a repeating 24 hour time interval. Here, the user must anticipate when hot water will be needed and set the timer accordingly.

This scheme has several limitations including the following. First, a user must predict when hot water will be needed and set the timer accordingly. Second, setting such timers is cumbersome and error prone. Third, these timers offer only a limited number of user selectable on and off events. Fourth, these timers do not distinguish usage patters that differ with the day of the week or month. Fifth, these timers do not learn the habits of hot water users. And finally, these timers have limited resolution and accuracy.

Often hot water will be needed at a time other than when pump operation is scheduled. Such events may entirely unpredictable or they may reflect a gradual or sudden change in the user's hot water demand habits. In other cases, the user's hot water demands may simply differ based on day of the week or for holidays.

Timer systems will also activate at times when hot water is not needed, as during vacations. This uncertainty in predicting when hot water is needed leads users to set the pump to run for much longer periods than the period of actual demand. This wastes energy for water heating and for pump operation.

In addition, the timer will lose its time setting if electrical power is lost. In addition, timers do not compensate for changes in daylight savings time or sunrise and day length, all of which can affect a usage schedule and may cause the pump to operate at times when hot water is not needed, or to not operate when needed.

Some systems attempt to supply hot water only when a user desires hot water. Such manually activated demand systems require a user to request hot water by operating a switch that activates a pump. To be useful, these systems require switches located near each remote outlet.

Manually activated demand systems also suffer from various limitations. Users must be trained to activate a manual device and to open the hot water outlet valve or faucet at the appropriate time. Such devices are unfamiliar and children or guests may have difficulty obtaining hot water. Manually activated water demand switches must be located near each remote hot water outlet, often requiring extensive wiring between each device and the pump. Remote activation devices require power, supplied either by wiring connections, or by batteries that must be changed periodically. Where batteries are used, a failed battery causes the system to become inoperative and its benefit is lost.

What is needed is a simple control system that solves these problems by obtaining and analyzing temperature, time, and hot water system data to optimize the process for selecting the periods during which the pump will run.

SUMMARY OF THE INVENTION

An improved system and method for detecting and anticipating fluid demand from a pipe has been found.

In the present invention for detecting fluid demand a first pipe transports a fluid, a sensor senses a temperature varying with the temperature of the fluid, a processor in signal communication with the temperature sensor evaluates a time rate of temperature change, and a current flow in an electrical circuit is responsive to the time rate of change of temperature.

In an embodiment, the processor makes a plurality of temperature measurements corresponding to different times and calculates at least one temperature difference between a first temperature measured at a first time and one or more second temperatures measured at one or more respective second times where each of the times is bounded by a single preselected time interval and the current flow in the electric circuit occurs when one of said temperature differences as compared to a respective trigger value indicates that fluid has been demanded from the pipe. In some embodiments, a plurality of temperature differences are measured within the preselected time interval. And in some embodiments the processor updates at least one trigger value based on a comparison of the trigger value to historical temperature differences inferred from data saved in a memory device that is in signal communication with the processor. In yet other embodiments, the preselected time interval is in the range of about 0.1 to 15 seconds and the trigger values lie in a range of about 0.001 to 100 degrees Fahrenheit. In another embodiment, the sensor is a non-contact temperature sensor such as an infrared sensor.

In some embodiments the first pipe is a hot water pipe in a hot water circuit, the hot water circuit is in fluid communication with a pump and a valve, the sensor senses temperature at a location on the outer surface of the first pipe, and the valve is operative to demand hot water from the hot water circuit and the electric power circuit is operative to actuate the pump in response to the hot water demand. In some embodiments, the sensor is an infrared temperature sensor and invention includes a means for deactivating the pump. And in some embodiments the processor saves in a memory device an indication of at least a first time on a first day when hot water is demanded from the hot water circuit and the processor actuates the pump on a second day subsequent to the first day at a second time which differs from said first time by a first predetermined time difference. And in an embodiment, on a day subsequent to the first day the processor makes the first time indication previously saved in the memory device ineffective to actuate the pump when hot water is not demanded between a fourth time and a fifth time, said fourth and fifth times differing from said first time by respective second and third predetermined time differences. In an embodiment the pump is a recirculation pump.

And in some embodiments, the first pipe supplies cold water to a water heater, a second pipe is a hot water pipe in a hot water circuit, the hot water circuit is in fluid communication with the water heater, a pump and a valve, the sensor senses the temperature at a location on the outer surface of the first pipe, said location being proximate to said hot water heater and the valve is operative to demand hot water from the hot water circuit and the electric circuit is operative to actuate the pump in response to the hot water demand. In an embodiment the sensor is an infrared temperature sensor and the invention includes a means to deactivate the pump. In some embodiments the processor saves in a memory device an indication of at least a first time on a first day when hot water is demanded from the hot water circuit and the processor actuates the pump on a second day subsequent to the first day at a second time which differs from said first time by a first predetermined time difference. And in some embodiments on a day subsequent to the first day the processor makes the first time indication previously saved in the memory device ineffective to actuate the pump when hot water is not demanded between a fourth time and a fifth time, said fourth and fifth times differing from said first time by respective second and third predetermined time differences. In an embodiment the pump is a recirculating pump.

And an embodiment includes a sensor for sensing a temperature that varies with the temperature of the fluid, a processor in signal communication with the temperature sensor and a time base, the processor for making a plurality of temperature measurements corresponding to different times and for calculating at least one temperature difference between a first temperature measured at a first time and one or more second temperatures measured at one or more respective second times subsequent to said first time where each of the times is bounded by a single preselected time interval; and, the processor causes an electrical current to flow in an electric circuit when one of said temperature differences as compared to a respective trigger value indicates that fluid has been demanded from the pipe.

In still another embodiment, the pipe is in fluid communication with a hot fluid source and the sensor is an infrared temperature sensor located adjacent to the pipe and proximate to the hot fluid source.

In yet another embodiment the present invention carries out the steps of transporting hot water in a first pipe in fluid communication with a potable hot water source and a hot water valve, measuring a plurality of temperatures corresponding to different times with an infrared temperature sensor in signal communication with a processor said temperatures being measured at a location on an outer surface of a second pipe transporting cold water to the hot water source, varying the temperature of the location on the outer surface of the second pipe by opening and closing the valve, calculating a time rate of temperature change and signaling a recirculating pump to transport water from the first pipe to the hot water source when the time rate of temperature change exceeds a preselected trigger value.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying description provides in combination with the specification and the claims a description of the invention:

FIG. 1 is a block diagram that illustrates components and interconnections of an embodiment of the present invention;

FIG. 2 is a schematic drawing of a representative hot water delivery system;

FIG. 3A is a diagram schematically illustrating a typical hot and cold water piping system;

FIG. 3B is a diagram illustrating aspects of a typical hot and cold water piping system with a recirculation pump;

FIG. 3C is a diagram illustrating several prior art approaches to control of a recirculation pump;

FIG. 3D is a diagram of a plumbing system with a recirculation pump located at an outlet;

FIG. 3E is a diagram of a plumbing system illustrating sensor locations according to embodiments of the descriptions herein for controlling a recirculation pump;

FIG. 4 shows temperature vs. time data plots illustrative of rates of change and sequencing in a hot water system;

FIG. 5A, 5B, 5C are flow charts of embodiments according to the descriptions herein;

FIG 6 is a state transition diagram of an embodiment of a control strategy.

DETAILED DESCRIPTION OF THE INVENTION

While specific embodiments are discussed below, it should be understood that this is done for illustration purposes only and that other components and configurations can be used in accordance with the systems and methods described herein without departing from the spirit of the invention.

FIG. 1 shows a block diagram of an embodiment of a system 100 according to the present invention. Plumbing system sensing 101 comprises one or more sensors measuring or detecting properties of the plumbing system. These properties are of interest in controlling a hot water recirculation pump. These properties can include, for example, temperature, pressure, flow, or vibration at various points in the household or building plumbing system. In some embodiments one property of interest is derived from measuring another physical phenomenon, for example temperature or vibration can indicate flow. A variety of sensors can be used in various embodiments, all according to the present invention. A temperature sensor, for example, can employ a thermistor, a thermocouple, or an infrared-sensitive device. In one embodiment, temperature is sensed using a thermistor of type 103AT commercially available from several vendors.

In another embodiment, temperature sensing is accomplished using a non-contact sensor. A non-contact sensor measures the temperature of a surface without physical contact with the surface. Such a sensor can operate by measuring radiant energy or infrared emissions of a surface. An example of such a sensor is an infrared thermopile detector manufactured by Melexis of Belgium, type MLX90247. An advantage of a non-contact sensor is that it has very low thermal mass and can therefore respond quickly to changes in sensed temperature.

In one embodiment, the rate of change of temperature at the outside surface of a location in a piping system is used to detect flow of fluid through the inside of the pipe. In one embodiment, this flow indicates demand for the fluid at a remote location.

Connection 102 provides data from the sensors to the processor 105. Connection 102 can be of suitable length to allow the sensors to be located as needed within the plumbing system while remaining at a proximate location. For example, in one embodiment a temperature/flow sensor is located to sense the surface of a hot water delivery pipe near the outlet of the hot water heater and a pair of wires connects the sensor to the controller. In another embodiment a temperature/flow sensor is located at the return of a recirculation system into a hot water heater. In one embodiment a temperature/flow sensor is located to sense the surface of a cold water pipe providing water to the hot water heater. In one embodiment, connection 102 can be implemented as a wireless connection.

Display 103 is used to indicate information to the user. Information can include for example, status, faults, and system modes. In one embodiment display 103 is a multi-line character display, such as a liquid crystal display (LCD). In another embodiment, the display 103 is an array of light emitting diode (LED) devices. These may be any combination of single color or multi-color LEDs. Multi-color LEDs can be made to change color under processor command, thus using color to indicate information to the user. LEDs can also be made to glow steady, blink, or flash in various patterns to communicate to an observer, all under command of the controller 105. In one embodiment display 103 is a single monochromatic LED that uses various modes of steady-on, steady-off, or patterns of on and off to indicate information. Connection 104 provides signals to the display 103 from the controller 105.

Processor 105 controls the various outputs of the system in response to predetermined algorithms and in response to data that can include input from sensing system 101 as well as time rate of change and histories of sensed parameters. The outputs of the processor 105 can include setting the power switch 114 to an off or on state, driving the display 103, and setting the state of the remote pump connection 117.

The processor 105 can be implemented in many ways, all in accordance with the descriptions herein. The processor can also be described by terms such as controller, microcomputer, digital computer, analog computer, or threshold detector. In one embodiment processor 105 is a collection of analog electronics. Control algorithms are implemented by selection of components, circuit topology and operational amplifiers and comparators.

In another embodiment, processor 105 includes a digital microcontroller or processor executing a set of instructions stored in memory. The set of instructions are sometimes referred to as software, firmware, or a program. The processor executes software that implements predetermined sensor data gathering, decision, and control algorithms. In one embodiment the processorer function is provided by a PIC16F676 microcontroller combined with support circuitry. The PIC16F1676 is manufactured by the Microchip corporation of Santa Clara, Calif.

In one embodiment a time base is included in processorer 105. A time base can provide measurements of intervals and is useful in determining rate of change of a value over a time interval. A time base can be implemented using digital components such as counters or timers. A time base can also be implemented in non-digital or analog circuit, for example by observing the time varying voltage of a charging capacitor.

In one embodiment processor 105 can perform functions requiring storage of parameters or events. A memory 107 and data storage and retrieval means 106 is provided to accomplish these functions. In one embodiment the memory 107 and controller 105 are contained in a single integrated circuit along with interconnection 106. In another embodiment the memory 107 is in a separate package from processor 105. Several types of memory 107 may be provided, all in accordance with the present invention, including random-access memory (RAM), electrically erasable programmable memory (EEPROM), FLASH memory, disk storage, or any other means providing for storage and retrieval of data by the controller 105. In one embodiment the memory contains software for the controller that can be changed without removal or replacement of the memory. Thus the controller program and associated algorithms can be easily changed, for example to fix problems, add features, improve software, or modify algorithms or constants.

The system 100 is connected to a source of electrical power by input power connector 112. The power is made available within the system by power wiring 113. Power wiring 113 brings the input power to power supply 109, phase detector 111, and the input of power switch 114. Power supply 109 provides power to the components of the system. Power connections from power supply 109 to individual components are not shown in FIG. 2 to simplify the diagram.

In one embodiment, the power input 112 is connected to a source of 120 volt, 60 Hz. alternating current (AC) commonly available in the United States and other countries. The power supply converts one hundred twenty volts AC to five volts direct current (DC) usable by controller 105, sensors 101, display 103, memory 107 and phase detector 111.

Control of an external pump is provided by controllable power switch 114. Power switch 114 can be turned on or off by processor 105 using connection 110. When power switch 114 is set to the on state, the output power wiring 115 is energized and power is available at output power connector 116. In one embodiment current flows through circuit 114 in response to demand detected using time rate of temperature change. In one embodiment the connector is a receptacle into which a power cord for an external device can be connected. For example, a recirculation pump power cord can be connected. In another embodiment, the pump controller 100 is integrated into the pump mechanically and electrically so that pump power output 116 is wired directly to the pump. In one embodiment, power switch 114 is a solid state relay, model number PR21HD2NSI, manufactured by the Sharp Corporation.

In some situations it is desirable to provide a signal 117 to external systems that is activated simultaneously when the power switch 114 is commanded to the on state. A remote pump activation signal 117 is provided for this purpose. Thus signal 117 is an electric circuit responsive to time rate of temperature change. Signal 117 may be a voltage-level signal, switch closure, pulse, relay output, open collector transistor, or any control signal appropriate for activating the desired remote device. In one embodiment, current flow in circuit 117 signals hot water demand.

Phase detector 111 is provided in certain embodiments, where the input power supply 12 is a source of alternating voltage. The phase detector 111 can provide several features to the system. In one embodiment, the phase detector 111 derives a periodic clock signal from the repetitive alternating cycle of the input power source by detecting certain repetitive phase characteristics of the input power at connector 112 and wiring 113. An example of such a characteristic is a zero crossing, in which case the phase detector may also be called a zero crossing detector.

In one embodiment the phase detector 111 detects zero crossings of a 60 Hz. sinusoidal voltage to produce a 120 Hz clock signal. A clock signal is produced each time the input crosses zero voltage. A 60 Hz sinusoidal voltage crosses zero 120 times each second. The power input frequency is often very accurate and stable, and a clock derived from the power frequency can be very accurate. The controller 105 can use an accurate clock for many functions.

Another feature that can be provided by phase detector 111 and controller 105 is activation or deactivation of the pump via control switch 114 at certain phase angles of the AC power supply. It can be desirable to activate the pump at zero voltage, peak voltage, zero current, or some other selected phase angle of a sinusoidal AC voltage or current input. Activation of the pump at selected phase angles can reduce interference, extend pump life and provide other benefits.

In one embodiment, pump switching at a desired phase angle of the AC input waveform is provided by a zero crossing detector combined with an interval timer. The phase detector 111 detects zero crossings of the input power and then waits a predetermined period of time to switch the pump. For example, if it is desired to switch at the peak of a 60 Hz waveform, it can be calculated that the peak voltage magnitude occurs approximately 4.17 milliseconds after each zero crossing.

FIG. 2 shows a schematic drawing of some elements of a hot water delivery system to illustrate how a temperature sensor can be used to detect flow of hot water near the sensor. Although only a limited number of outlets and limited piping is shown, this is a simplification for illustration. An actual system may contain many more outlets and other elements not shown here.

With reference to FIG. 2, a system 200 is shown for delivery of hot water to outlets 205. 206 and 207. Pressurized cold water enters the system through cold water piping 201 and flows into the hot water heater 202. Typically heater 202 includes a storage tank and heating element or burner for heating water and a temperature regulator, but for this illustration the important function is that heater 202 provides a source of heated water. Hot water piping 203 carries water from the heater 202 to locations where hot water is needed, such as sinks, showers, bathtubs, laundry. For illustration three outlets are shown: outlet 206 is controlled by valve 205, outlet 208 is controlled by valve 207, outlet 210 is controlled by valve 209. The hot water piping system may continue past piping node 211, and may include other outlets or a recirculation system returning the hot water to the hot water heater 202.

A temperature sensor 204 is placed on the hot water piping 203 at a location where it is desired to detect flow of hot water according to the present invention. This sensor measures the outside surface temperature of the pipe and can be mounted without cutting or modifying hot water piping 203 in any way.

When a user desires hot water, he or she opens the valve (e.g. 205, 207, 209) corresponding to the location where water is desired and hot water flows from the heater 202, through piping 203, to the outlet (206, 208, 210) corresponding to the opened valve.

When hot water is not being demanded, i.e. none of the valves 205, 207 or 209 are opened, water in hot water piping 203 cools because after the hot water and pipe are typically hotter than the surrounding ambient temperature and heat is radiated or conducted away. Thus the temperature measured by sensor 204 decreases over time when there is no demand for hot water.

When hot water demand is subsequently indicated by a user opening one or more of valves 205, 207 or 209, hot water will flow from heater 202 into piping 203 and past sensor 204. This water will typically be at a higher temperature than the water in the pipe when no demand is present. Thus the hot water flow caused by demand will cause the pipe 203 temperature to rise along the path of water flow. This will cause a rise in temperature at sensor 204 over time. In this way time rate of change of temperature at sensor 204 can be used to detect demand for hot water.

A key aspect of this scheme is that only the rate of change of the measured temperature is needed. The temperature value itself is not important. In one embodiment, the temperature sensor is not calibrated and no temperature value is calculated in conventional units such as Fahrenheit or Celsius. The sensor is used only to note rate of change over time.

In one embodiment, the temperature sensor is a thermistor. Thermistors change resistance with temperature. The resistance as a function of temperature for a thermistor is typically monotonic but non-linear, requiring conversion to a linear scale when a temperature value is needed in conventional units. But according to the present embodiment, absolute temperature is not needed, thus the non-linearity of the sensor is not significant. This allows use of less expensive sensors and requires less signal processing of the sensed value when it is desired to detect demand for input to a controller.

In another embodiment, the temperature sensor is a non-contact sensor such as a device sensitive to infrared radiation on a surface not physically touching the sensor.

The scheme just described can also be used as a simple but effective communication mechanism. This communication system uses the flow of hot water as the signaling medium. The valve is the sending device and the temperature sensor the receiving device. For example, again with reference to FIG. 2, a user at valve 209 wishes to send a discrete message to the remote location where the temperature sensor 204 is mounted. The user opens valve 209 for a short time, allowing water to flow from heater 202, through piping 203 and exit outlet 210. As described above, this will cause temperature sensor 204 to be subjected to a positive rate of change of temperature. This change of temperature can be matched to various profiles to ascertain it is the result of a user opening a valve and not other causes. Thus other cause of temperature change can be ignored, such as ambient temperature change or heating when the hot water heater 202 heats the tank by activating its burner or heating element. Thus a reliable communication mechanism is established from each location where hot water may be used (206, 208, 210) to the remote location of the temperature sensor.

In one embodiment, this communication mechanism is used to signal a demand for hot water. According to this embodiment, a user who desires hot water opens a valve at the location where hot water is desired, allows a small amount of water to run, then closes the valve. This sends a message to the temperature sensor 204 that is in turn used to activate a hot water delivery system. The user, after opening and closing the valve to send the hot water request, waits for a short period of time for the hot water recirculation system to supply hot water. The user than opens the valve and uses hot water normally.

In this manner, any valve, faucet, or tap outlet of a hot water system can be used both to obtain hot water and also to signal a hot water delivery system indicating that hot water use is desired.

This scheme has several advantages. No special installation is required on conventional systems. The signaling device, i.e. the faucet, is a component of conventional plumbing systems and requires no additional components, power source, or redesign. The receiving device is easily installed on existing piping by attaching to the pipe exterior surface and requires no plumbing or modification. No wiring is required to connect the receiver to the transmitter.

In addition, the system is easy to learn to use as the actions required are part of the familiar process of using hot water at a conventional outlet. Another advantage is that the system can be used in a conventional manner or by a person untrained in using the faucet as a signaling device. In this way an untrained person or unfamiliar guest can open a faucet and let it run and the receiver will detect demand and receive hot water promptly.

It can be appreciated that there are many ways to detect demand for a fluid in a fluid supply system because demand causes flow of fluid past many locations in the system.

FIGS. 3A, 3B, 3C, 3D and 3E all show schematic diagrams of plumbing systems upon which the improved systems and methods described herein may be practiced.

FIG. 3A shows a schematic diagram of a plumbing system 300 supplying hot and cold water to a variety of locations. The system 300 of FIG. 3A does not include a path for hot water recirculation.

With reference to FIG. 3A, cold water enters the system 300 at point 301 under pressure. Cold water from supply 301 is routed by plumbing to both cold water distribution piping system 302 and to hot water heater 303, designated in the drawing by “HW.” Hot water heater 303 raises the temperature of the water and supplies hot water to hot water distribution piping system 304. At various locations hot and cold water is delivered to users and appliances. Three representative locations are shown in FIG. 3A, 305, 306, 307. The number and distribution of locations can vary widely in actual systems, as can the piping layout. A simplified layout is illustrated in the Figure. At each location 305, 306, and 307 a connection to hot water piping system 304 and cold water piping system 302 convey water to the location of usage 305, 306 or 307. At each location of usage, set of valves, designated “V” in the drawing, controls the flow of hot and cold water from the piping system.

FIG. 3B shows a system 320 identical to system 300 of FIG. 3A, with the exception that a recirculation extension is included in system 320. In system 320 an additional plumbing line attaches at a point 321 of the hot water plumbing system. The point of attachment 321 is selected to include as much of the hot water distribution system as possible between hot water heater HW and point 321. The recirculation plumbing extends from point 321 and returns to hot water heater HW at point 324. In the figure hot water return 324 is shown as a separate conduit into the hot water heater. Other systems route this connection to the cold water supply lines. Pump 324 is often included to move water from point 321 to 324. Pump 324 may run continuously or be regulated by a number of control schemes.

Not shown in system 320 are a number of check valves sometimes installed to prevent water flow in inappropriate directions in the system. Those familiar with the art will readily identify locations and functions for these valves.

FIG. 3C illustrates schematically a number of prior art approaches to control of a hot water recirculation pump that are improved upon by the systems and methods described herein. The system 340 of FIG. 3C is identical to system 320 of FIG. 3B but now includes representations of several control and sensor configurations. It should be noted that in a typical system only some of the sensors and controls shown here are employed.

With reference to FIG. 3C and system 340, a controllable pump 341 moves hot water in a recirculation system. In one prior art approach, the pump is controlled by a timer device 342. In another prior art approach, the system uses temperature regulation controlled by a temperature sensor, designated by “T” in the Figure. A local temperature sensor 346 may be used, where the sensor is near the pump 341 and return point of the recirculation system. Alternatively a remote temperature sensor 347 may be used, where there is significant separation between pump 341 and sensor 347.

In another prior art approach, still with reference to FIG. 3C, switches or sensors, designated as “S” in the Figure, are located near each location where hot water may be used. Sensors 343, 344, 345 can be manually activated, coupled to faucet motion, or sensors of the presence or motion of bodies in a room near a water outlet. These sensors cause the pump to activate.

FIG. 3D illustrates another approach found in prior art recirculation systems. The system 360 shown in FIG. 3D is identical to system 300 in FIG. 3A, except a recirculation system has been added. This recirculation is different from that shown in system 320 in FIG. 3B. In system 360 the recirculation system consists of a hot water diversion pipe 361, a pump 362, and a return pipe 363, all located at an outlet location at or near the furthest point from the hot water heater HW in the plumbing system. Pump 362 removes hot water from hot water supply by means of pipe 361 and returns water to the cold water supply by means of pipe 363. Thus the action is similar to system 320 of FIG. 3B, but installation near an outlet can be desirable.

FIG. 3E is illustrates an embodiment of the system and methods described herein. The system 380 of FIG. 3E is identical in plumbing to system 320 of FIG. 3B, except that it now includes an improved control scheme. An embodiment of the systems and methods described herein can be applied to many system configurations and topologies, including that in system 360 in FIG. 3D.

It can be appreciated that there are many sensor configurations and locations that can be used to detect flow in a plumbing system, and that not all possible sensors will be present in every embodiment. Referring to FIG. 3E, in system 380, sensors 381, 382 and 383 are shown as possible sensor locations. Systems can employ one, any two, or all three sensors in the spirit of the present invention. For example, a flow sensor 381 can detect demand for hot water. In one embodiment this flow is detected by rate of change of the output of temperature sensor 381. Sensor 381 can be used in conjunction with processor 384 to detect flow of water and activate the pump P by means of closing power switch 385.

Sensor 381 can be located on a pipe in the hot water system proximate to the outlet of the hot water heater HW. A location is proximate if it allows the sensor to detect flow promptly and reliably. For a typical structure there are many proximate locations on the contiguous plumbing network.

In one embodiment sensor 382 detects flow of hot water in the return piping segment of the recirculation system. Sensor 382 can be a temperature sensor used in conjunction with processor 384 to open switch 385 and stop pump P when hot water has filled the system. Sensor 382 is shown close to pump P, but may be located at any point in the hot water system needed. Generally the location of sensor 382 is chosen to include all outlets between the sensor and hot water heater. In many systems ease of installation makes it desirable to install sensor 382 proximate to the pump or to the hot water heater.

In one embodiment, sensor 382 is used in conjunction with controller 383 to detect that the pump should be shutoff by noting a positive temperature rate at sensor 382, followed by a near-zero temperature rate at sensor 382.

In another embodiment, sensor 383 detects hot water demand. Sensor 383 is mounted proximate to the cold water inlet to hot water heater HW. Such a sensor can be used to detect hot water demand since the exit of hot water from the hot water heater is replaced by an inflow of cold water flowing by sensor 383. The cold water flow can be detected by the negative rate of temperature change at sensor 383.

FIG. 4 is used to further describe embodiments of a hot water recirculation pump control algorithms according to the system and methods described herein. FIG. 4 shows a plot 400 of data at two locations in a hot water circulation system, data plot 401 and data plot 402. The data plots 401 and 402 can be values read from the sensors plotted against a linear time scale. Because the techniques described do not rely on specific time or data values, these are not noted in plot 400.

In one embodiment, sensors producing data for plots 401 and 402 can be temperature sensing devices. However it is a significant feature that the methods described rely on changes in temperature, and this can be executed without regard for actual temperature values in conventional units, such as Fahrenheit or Kelvin. It is also a feature that the controller does not rely on set points expressed in conventional units.

With regard to plot 400, three instants of times are called out: t_(X) 403, t_(Y) 404 and t_(Z) 405. Plot 401 shows the temperature of a location near the outlet of a hot water heater, as sensor 381 in FIG. 3E. Plot 402 shows the temperature of a location near the return of a hot water recirculation system, as sensor 382 in FIG. 4E.

In FIG. 4, at time t_(X) 403, a positive rate of change is seen in data plot 401, indicating flow of hot water out of the hot water heater. Although the rate of change shown in plot 401 is linear for illustration, it may have higher-order components or be non-linear. A feature is that the invention described herein can be configured to distinguish changes due to hot water demand from changes due to other sources, for example ambient temperature rise, or hot water heater burner or element activation. Thus the flow of water indicated in plot 401 at time t_(X) 403 indicates demand for hot water. Accordingly the recirculation pump is activated.

At time t_(Y) 404 a positive rate of change is seen at the return path of the recirculation line, as can be seen in plot 402. This indicates some hot water is being returned to the hot water heater and that the hot water circuit is nearly filled with hot water due to the preceding activation of the recirculation pump.

At time t_(Z) 405 the hot water return line plot 402 has reached a steady temperature after a rising temperature starting at time t_(Y) 404, indicating the system has reached a steady-state maximum temperature. At this point in time the hot water supply line and recirculation line are filled with hot water.

In one embodiment, the control strategy described above is implemented by use of two temperature sensors, one placed to sense the data corresponding to plot 401, and the other corresponding to plot 402. Thus the control strategy can be executed as described.

In another embodiment, the control strategy described above is implemented using a single sensor, at a location corresponding to plot 401. This embodiment uses the data from sensor location corresponding to plot 401 to start the pump in response to demand, and uses an estimate of the time required to fill the system with hot water, shown as t_(PUMP) 406 in plot 400 to determine when to turn off the pump. In one embodiment, the estimate of t_(PUMP) is predetermined.

In another embodiment the system is initially installed connected with two sensors, allowing measurement and storage of system parameters such as t_(PUMP) 406. If a sensor at location corresponding to plot 402 subsequently fails, the system can continue to operate using sensor at location corresponding to location 401 and previously measured t_(PUMP) 406.

A problem can arise when using analog-to-digital converters for measuring rates of change over time. Analog-to-digital converters only provide a limited number of discrete spaced input voltage detection levels, each corresponding to a numerical output value. For a slowly changing signal, i.e. a low rate signal, the signal may not change enough between samples to cause the numerical output value to change. The samples can be taken further apart in time, but this slows down the detection for rapidly changing signals.

The present invention can overcome the problems with conventional analog-to-digital conversions calculating rates described above. In one embodiment the processor makes temperature measurements continuously and stores a number of the most recent samples. Then several differences are calculated. In one embodiment the change over the last sample period, the last two sample periods, and the last four sample periods are all calculated. The difference between a more recent sample and the latest sample provides fast detection of rapidly changing signals. Differences between the latest sample and data samples further in the past detects slowly changing signals that may take several sample periods to change enough to cause the digital output of the analog-to-digital converter to change significantly.

In another embodiment, the sensor data 402 shown in FIG. 4 can be used to implement a self-adjusting temperature regulation algorithm. In this mode, the pump shuts off at time t_(Z) 405, when the return temperature has reached a steady-state value. The steady-state value is then also stored as the desired setpoint for system control in temperature regulation mode. This scheme has the advantage of being adaptive, in that the temperature setpoint can be reset each time the pump is activated, automatically adapting for changes in environmental conditions or system aging. This method also has the advantage of using raw sensor values as setpoint, avoiding any requirement for conversion to conventional unit systems or manual temperature setpoint setting.

As described herein, both a temperature-regulated and a demand regulated control mode can be implemented to control a recirculation pump. Each mode can be desirable in certain situations. Temperature regulated mode provides ready hot water, but wastes energy in periods of no demand. Demand regulated mode saves energy but requires slightly longer for delivery of hot water, as compared to temperature regulated mode.

A solution is to provide a controller able to execute the algorithms of both modes, with additional functionality provided to select between the modes and transition between the modes, a multi-mode controller. One embodiment of this multi-mode control scheme is illustrated in FIG. 6. FIG. 6 provides a state-transition diagram, showing three system states 601, 603, and 606 as circles, and labeled lines 602, 604, 605, and 607 as conditions that cause transitions between the states. The controller is operating in exactly one of the states at any given time.

Economy, or demand-controlled mode state 601 executes when the pump is off and the system is awaiting a detected flow of hot water to activate the pump. This is an economical mode suited for most times. When demand is sensed, the controller traverses transition 607 and pump-on state 606 is executed, activating the recirculation pump.

Transition 604 is traversed when the hot water system is filled, or in one embodiment when a time limit has been exceeded. Transition 604 causes the controller to execute in temperature controlled-mode state 603. In temperature-controlled mode, the system can be activated by demand for hot water, or by falling temperature in the system, both conditions cause the controller to traverse transition 605. Thus in temperature controlled-mode hot water is readily available at all times.

After a predetermined period with no demand while in temperature-controlled mode state 603, the controller traverses transition 602 and executes demand-controlled mode state 601.

In one embodiments the predetermined time periods used as transition criteria for transitions 602 and 604 are determined as constants in the controller software program. In another embodiment, the time periods for transitions 602 and 604 can be adjusted during system operation in response to sensed conditions. Thus the time periods are adaptive over time.

In one embodiment, temperature controlled mode is selected for a period of time after pump activation and demand mode is selected after a period of time has elapsed with no demand. This is based on the principle that hot water is often used several times in near succession. Thus energy is saved in periods of no demand while hot water is readily available in periods of frequent demand.

FIG. 5A shows a flowchart describing one embodiment of a demand control mode using two sensors as described herein. At decision 501 it is determined that temperature is rising at a sensor near the output of a hot water heater. When temperature rise is positive, the pump is started in operation 502.

The pump runs until a rise in temperature is seen at the recirculation return, in decision 503. Following a rise, a steady-state value, or leveling-off, is waited for in decision 504. When temperature has reached a steady state value, it is recorded in operation 505, the pump is stopped in operation 506, and the controller returns to decision 501 awaiting demand once again.

FIG. 5B shows another embodiment, similar to FIG. 5A, but with several timers added to make the system more robust and provide additional functionality. Decision step 520 detects rising temperature near the outlet of a hot water heater, indicating demand and activates the pump in operation 521 then starts a timer in operation 522.

The system then waits for either a rising temperature in decision step 523 or the timer to reach a predetermined maximum value in decision 524. When either of the criteria in decisions 523 or 524 are satisfied, the algorithm proceeds accordingly.

If the maximum pump time is reached then decision 524 is true and operation proceeds to step 529, stopping the pump. The system then returns to step 520 to await demand.

Alternatively, if decision 523 is true because temperature is rising at the recirculation return, the controller then waits for either the rising temperature value to reach a steady-state value, satisfying the criteria in decision 526, or the maximum pump time to be reached in decision 528. If the maximum pump operation time is reached, satisfying decision 528, the pump is stopped in operation 529 and the controller returns to step 520.

Alternatively, if the temperature has reached a steady-state value, satisfying the decision criteria in decision 526, the controller then executes decision 527, determining if the pump has operated for a predetermined minimum time period. If the pump has not operated for the minimum time, the algorithm remains in decision 527 until the time period is complete. Eventually the time period will reach the predetermined value and the decision criteria 527 will be satisfied. The algorithm then proceeds to turn off the pump in operation 529 and return to decision 520 awaiting the next demand. In another embodiment, a delay is inserted between operation 529 and decision 520 to ensure a minimum time elapses between subsequent pump activations.

Another embodiment is illustrated in FIG. 5C. In this embodiment a demand sensor is used in combination with properties of the plumbing system. In one embodiment the properties of the plumbing system are estimated. In another embodiment the properties of the plumbing system used in the algorithm are selected to be effective for a variety of plumbing systems. In still another embodiment, the properties are measured and programmed into the controller.

With reference to FIG. 5C, decision block 530 is executed until demand is detected. Upon detection of demand, the pump is activated in step 531 and a timer is set and started in step 532. The timer setting value is the length of time the pump will run. This length of time is a parameter of the plumbing system. Decision block 533 is executed until the timer has completed.

When the timer has completed the pump is deactivated in step 534. In step 535 a timer is set and started. This timer serves to prevent the pump from restarting too soon after operating. In one embodiment this timer value can be zero so decision step 536 is essentially skipped. In other embodiments the timer value can be non-zero and decision block 536 is executed until the timer finishes.

After exiting decision block 536, the system returns to block 530 to await demand. In one embodiment an adaptive control scheme observes demand patterns and anticipates future demand based on past demand. It can be appreciated that this scheme can detect demand in many ways in accordance with the features and descriptions herein. For example, demand can be sensed by the flow sensors and algorithms described herein. Demand may also be detected by a motion detector, push button or other demand indication device.

In one embodiment, the system can include a timekeeping system. The timekeeping system generates a time-tag value that varies from 0-23 hours and recycles every 24 hours. The system can also generate a day-tag value that varies from 0-6 days and recycles every 7 days. This system is similar to a clock and calendar, but with significant differences. One way this system differs from a conventional clock and calendar is that it is not necessarily synchronized with any external or standard clock or calendar, but instead simply counts time from the moment power is first applied to the controller. In this way, a unique day-tag and time-tag is generated that can be used to store and recall controller events relative to one another, without reference to any outside time. This scheme has an advantage in that it does not require setting or synchronization to any outside clock. It also has the advantage of not requiring any adjustment for daylight savings time or time zones. Another advantage is that the system does not require any external interface, switches, buttons, or input devices since no external input is required for operation.

In one embodiment, the time-tag has a resolution of one minute, and the corresponding counter continuously counts from zero to 1439 and recycles, resuming the count from zero. There are 1440 minutes in a 24 hour period, thus a unique counter value is generated for each minute of a day. If the counter is observed at the same time of day on different days, it will have the same value. For example, if the time-tag counter value is 225 at 6 a.m. on Tuesday, it will have the value 225 at 6 a.m. on Wednesday and all days of the week until the controller loses power, within the accuracy of the counting system. Similarly, a day-tag counter will have a resolution of one day, so will count from zero to six and then recycle. For example, if the day-tag counter has a value of 3 on a certain Saturday, it will always have the value 3 on any Saturday.

The generation of time-tag and day-tag can be used to provide a capability for adaptive control. It is generally the case that hot water systems are used according to certain pattern of human behavior. It is an advantage that the system described herein can observe those patterns and control the recirculation system in accordance with the observed patterns.

For example, suppose the members of a family awaken and shower every weekday morning starting at times between 6 a.m. and 6:30 a.m. This can be determined by observing the pattern of demand for hot water during several days, correlated against time-tag and day-tag values. Thus the controller can activate the recirculation system so hot water is available each weekday at 6 a.m. Although the controller will not be aware that the time of activation is called 6 a.m. by those observing external clocks, it will be able to provide hot water at a consistent time each day. Similarly, the controller can be programmed to be aware that five of the seven days are weekend days, and to recognize and predict usage patterns accordingly.

Similarly it is a feature that the controller adaptive capability includes observation of variation from a pattern. In the above example, the members of a family begin to use hot water at times that vary between 6 a.m. and 6:30 a.m. on different weekdays. In one embodiment the controller is programmed to understand that these usage events on different days are related as variations on a morning usage pattern, and that the earliest event should govern the activation of the pump. 

1. A fluid demand detection device comprising: a first pipe for transporting a fluid; a sensor for sensing a temperature that varies with the temperature of the fluid; a processor in signal communication with the temperature sensor said processor for evaluating a time rate of temperature change; and, a current flow in an electric circuit responsive to the time rate of temperature change.
 2. The device of claim 1 wherein: the processor makes a plurality of temperature measurements corresponding to different times and calculates at least one temperature difference between a first temperature measured at a first time and one or more second temperatures measured at one or more respective second times; each of the times being bounded by a single preselected time interval; and, the current flow in the electric circuit occurring when one of said temperature differences as compared to a respective trigger value indicates that fluid has been demanded from the pipe.
 3. The device of claim 2 wherein a plurality of temperature differences are measured within the preselected time interval.
 4. The device of claim 3 wherein the processor updates at least one trigger value based on a comparison of the trigger value to historical temperature differences inferred from data saved in a memory device that is in signal communication with the processor.
 5. The device of claim 4 wherein the preselected time interval is in the range of 0.1 to 15 seconds.
 6. The device of claim 5 wherein the trigger values lie in a range of about 0.001 to 100 degrees Fahrenheit.
 7. The device of claim 6 wherein the sensor is a non-contact temperature sensor.
 8. The device of claim 6 wherein the sensor is an infrared temperature sensor.
 9. The device of claim 3 wherein: the first pipe is a hot water pipe in a hot water circuit; the hot water circuit is in fluid communication with a pump and a valve; the sensor senses the temperature at a location on the outer surface of the first pipe; and, the valve is operative to demand hot water from the hot water circuit and the electric power circuit is operative to actuate the pump in response to the hot water demand.
 10. The device of claim 9 wherein the sensor is an infrared temperature sensor.
 11. The device of claim 10 having a means to deactivate the pump.
 12. The device of claim 11 wherein: the processor saves in a memory device an indication of at least a first time on a first day when hot water is demanded from the hot water circuit; and, the processor actuates the pump on a second day subsequent to the first day at a second time which differs from said first time by a first predetermined time difference.
 13. The device of claim 12 wherein: on a day subsequent to the first day the processor makes the first time indication previously saved in the memory device ineffective to actuate the pump when hot water is not demanded between a fourth time and a fifth time, said fourth and fifth times differing from said first time by respective second and third predetermined time differences.
 14. The device of claim 13 wherein the pump is a recirculation pump.
 15. The device of claim 3 wherein: the first pipe supplies cold water to a water heater; a second pipe is a hot water pipe in a hot water circuit; the hot water circuit is in fluid communication with the water heater, a pump and a valve; the sensor senses the temperature at a location on the outer surface of the first pipe, said location being proximate to said hot water heater; and, the valve is operative to demand hot water from the hot water circuit and the electric circuit is operative to actuate the pump in response to the hot water demand.
 16. The device of claim 15 wherein the sensor is an infrared temperature sensor.
 17. The device of claim 16 having a means to deactivate the pump.
 18. The device of claim 17 wherein: the processor saves in a memory device an indication of at least a first time on a first day when hot water is demanded from the hot water circuit; and, the processor actuates the pump on a second day subsequent to the first day at a second time which differs from said first time by a first predetermined time difference.
 19. The device of claim 18 wherein: on a day subsequent to the first day the processor makes the first time indication previously saved in the memory device ineffective to actuate the pump when hot water is not demanded between a fourth time and a fifth time, said fourth and fifth times differing from said first time by respective second and third predetermined time differences.
 20. The device of claim 19 wherein the pump is a recirculation pump.
 21. A fluid demand detection device comprising: a pipe for transporting a fluid; a sensor for sensing a temperature that varies with the temperature of the fluid; a processor in signal communication with the temperature sensor and a time base; the processor for making a plurality of temperature measurements corresponding to different times and for calculating at least one temperature difference between a first temperature measured at a first time and one or more second temperatures measured at one or more respective second times subsequent to said first time; each of the times bounded by a single preselected time interval; and, the processor for causing an electrical current to flow in an electric circuit when one of said temperature differences as compared to a respective trigger value indicates that fluid has been demanded from the pipe.
 22. The device of claim 21 wherein: the pipe is in fluid communication with a hot fluid source; and, the sensor is an infrared temperature sensor located adjacent to the pipe and proximate to the hot fluid source.
 23. A method of detecting hot water demand comprising the steps of: transporting hot water in a first pipe in fluid communication with a potable hot water source and a hot water valve; measuring a plurality of temperatures corresponding to different times with an infrared temperature sensor in signal communication with a processor said temperatures being measured at a location on an outer surface of a second pipe transporting cold water to the hot water source; varying the temperature of the location on the outer surface of the second pipe by opening and closing the valve; calculating a time rate of temperature change; and, signaling a recirculating pump to transport water from the first pipe to the hot water source when the time rate of temperature change exceeds a preselected trigger value. 